1. Field of Invention
This invention relates to a method of sputtering with a sputtering apparatus for depositing a layer upon a substrate having a sputter target with a face exposed to substrate(s) and a magnetron providing a magnetic field that moves relative to the target face.
2. Description of Related Art
In most deposition processes that take place, for example in the formation of films on semiconductor wafers, one of the key manufacturing criteria is that there should be uniformity of deposited film thickness across the wafer. In particular for acoustic resonators, film thickness affects resonant frequency and therefore for all resonators upon a wafer to resonate at the same frequency, film thickness must be the same.
One of the key elements to achieve good uniformity of deposition upon a substrate from a closely spaced magnetron sputtering target assembly is the way in which the magnetic field moves with respect to the substrate (the alternative being large source-to-substrate distances approximating to a point source, but at the cost of low sputtering efficiency).
This may be achieved by moving the substrates past a static magnetron/target assembly. More recently, and particularly as substrate sizes have increased, the preference has been for the substrate to remain static and the magnetic field to move such as by physical rotation of the magnetron (or by suitable electrical switching causing the field of a fixed coil array to sweep across the face of the target). It is also known to move the field-creating element (e.g. a rotating magnet) laterally over a target and also to change target to magnetron spacing to improve uniformity of materials deposition thickness through target life (substrate to substrate repeatability). Whilst good results have been achieved using these techniques, and other techniques developed by the Applicants, lack of uniformity has still proved a significant problem in reactive sputtering processes.
It is important to recognise that it is the relative motion of magnetron to substrate that improves the deposition uniformity upon the substrate (by moving the point of erosion from the target—moving the source of sputtered material) not the motion of magnetron relative to the target—which achieves improved target consumption.
In the case of single wafer close coupled magnetron sputtering (as is commonplace in metallisation upon 100 mm-300 mm silicon wafers) there is generally a target little larger than the wafer (to minimise chamber size and target materials inventory) close coupled (to maximise efficiency of target utilisation) with a moving magnetron sweeping a magnetic field to gain uniformity of film deposition upon the substrate (and uniformity of target erosion).